Steering control unit with both flow amplification and manual steering capability

ABSTRACT

A fluid controller (17) is disclosed for controlling the flow of fluid to a steering cylinder (19). The controller includes a fluid meter (51) and a valving arrangement (49) including a valve spool (65) and a sleeve (67), which define a main fluid path including a main variable flow control orifice (121), the fluid meter (51), a variable flow control orifice (123), the steering cylinder (19), and a variable flow control orifice (125). In accordance with the invention, the spool and sleeve define an amplification fluid path including a variable amplification orifice (129) in parallel with the main fluid path, and disposed to amplify the flow of fluid through the meter. In one embodiment of the invention, the amplification fluid path communicates with the main fluid path upstream of the main variable flow control orifice, and at a location downstream of the fluid meter, but upstream of the variable flow control orifice (123). In order to facilitate manual steering using the fluid controller of the invention, the amplification orifice (129) reaches its maximum flow area when the spool and sleeve are still several degrees away from their maximum displacement. The amplification orifice then decreases and closes as the spool and sleeve reach maximum displacement. As a result, the amplification fluid path is closed at maximum valve displacement, and therefore does not act as a short-circuit, making it impossible to manually steer.

BACKGROUND OF THE DISCLOSURE

The present invention relates to fluid controllers of the type used tocontrol the flow of fluid from the source of pressurized fluid to afluid pressure operated device, such as a steering cylinder.

A typical fluid controller of the type to which the present inventionrelates includes a housing which defines various fluid ports, andfurther includes a fluid meter and valving, and an arrangement forimparting follow-up movement to the valving in response to flow throughthe fluid meter. The flow through the controller valving is directlyproportional to the area of the main variable flow control orifice,which, in turn, is proportional to the rate at which the steering wheelis rotated. Furthermore, the area of the main variable flow controlorifice has a know relationship to the displacement of the controllervalving.

Therefore, it has long been an object of those skilled in the art toprovide a steering system, including a fluid controller, in which thetotal flow through the steering system is substantially greater than theflow through the controller, but with the overall system flow beingrelated to the flow through the controller in a known manner. See forexample U.S. Pat. No. 4,052,929 in which the controller receives fluidfrom one pump and generates a pilot signal to control a pilot operatedvalve which receives fluid from a second pump. The total steering flowcomprises the flow through the pilot operated valve plus the flow fromthe controller. Such a system is theoretically satisfactory, but thecost of such a system becomes nearly prohibitive because of the additionof the pilot operated valve and the second pump.

More recently, there has been an attempt to provide a flow to thesteering cylinder which is greater than the flow through the fluid meterby having the full amount of desired steering flow enter the controller,with one portion flowing through the controller valving and fluid meterin the normal manner, and the remainder of the fluid flowing through apressure regulating device and a bypass throttle. These two portions offluid recombine within the controller and flow to the steering cylinder.See U.S. Pat. No. 4,566,272. It is possible that the performance of acontroller made in accordance with U. S. Pat. No. 4,566,272 would besatisfactory, however, the addition of a pressure regulating valvewithin the controller, and the associated structure would still addsubstantially to the cost of the controller, and in many applicationswould require substantial redesign of at least the controller housing inorder to accommodate the addition of such a valve.

U.S. Pat. No. 4,759,182, assigned to the assignee of the presentinvention, discloses a fluid controller in which the valving defines anamplification fluid path, including a variable amplification orifice inparallel with the main fluid path. Thus, the amplification fluid pathprovides an amplification ratio which can be made to vary, in anydesired manner, as a function of valve displacement. It has beendiscovered, however, that when the amplification fluid path of U.S. Pat.No. 4,759,182 is applied to fluid controllers which are capable of amanual steering operation, any attempts to manually steer the vehicleare unsuccessful. More specifically, rotation of the steering wheel doesnot result in the buildup of pressurized fluid which is communicated tothe steering cylinder to effect the manual steering operation.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved steering system and fluid controller, wherein the controllerhas the capability of providing an amplified steering flow, but in whichthe fluid controller is capable of manual steering operations.

The above and other objects of the present invention are accomplished byproviding an improved controller of the type including housing meansdefining an inlet port for connection to the source of pressurizedfluid, a return port for connection to a reservoir, and first and secondcontrol fluid ports for connection to the fluid pressure operateddevice. Valve means is disposed in the housing means and defines aneutral position and a first operating position. The housing means andthe valve means cooperate to define a main fluid path communicatingbetween the inlet port and the first control fluid port, and between thesecond control fluid port and the return port when the valve means is inthe first operating position. A fluid actuated means imparts follow-upmovement to the valve means, proportional to the volume of fluid flowthrough the fluid actuated means, which is disposed in series flowrelationship in the main fluid path, between the inlet port and thefirst control fluid port. The main fluid path includes a first variableflow control orifice disposed between the inlet port and the fluidactuated means, and having its minimum flow area when the valve means isin the neutral position, and an increasing flow area as the valve meansis displaced from the neutral position toward the first operatingposition. The main fluid path includes a second variable flow controlorifice disposed between the fluid actuated means and the first controlfluid port. The housing means and the valve means cooperate to define anamplification fluid path, in parallel with the main fluid path. Theamplification fluid path is in communication with the main fluid path ata first location disposed between the fluid inlet port and the firstvariable flow control orifice, and at a second location disposed betweenthe fluid actuated means and the first control fluid port. Theamplification fluid path includes a variable amplification orificehaving a substantially zero flow area when the valve means is in theneutral position, and an increasing flow area as the valve means isdisplaced from the neutral position toward the first operating position.The main variable flow control orifice begins to open at least as soonas the variable amplification orifice, as the valve means moves from theneutral position toward the first operating position. The main variableflow control orifice has its maximum flow area when the valve means isdisplaced from the neutral position to a maximum displacement position.

The improved controller is characterized by the variable amplificationorifice reaching its maximum flow area when the valve means is displacedfrom the neutral position to the first operating position, which issubstantially less than the maximum displacement. The variableamplification orifice changes from its maximum flow area to thesubstantially zero flow area as the valve means is displaced from thefirst operating position to the maximum displacement position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydraulic schematic of a load sensing, hydrostatic powersteering system of the type with which the present invention may beutilized.

FIG. 2 is an axial cross-section of a fluid controller of the type towhich the present invention relates.

FIG. 3 is a unidirectional flow diagram illustrating the fluidcontroller shown schematically in FIG. 1, as well as the variousorifices shown in FIG. 1.

FIG. 4 is an overlay view of the valving used in the fluid controllershown in FIG. 2, with the valving in the neutral position, but on alarger scale than in FIG. 2.

FIGS. 5-7 are enlarged, fragmentary overlay views, similar to FIG. 4,but with the valving displaced from the neutral position.

FIG. 8 is a flow diagram, similar to FIG. 3, illustrating an alternativeembodiment of the present invention.

FIG. 9 is a graph of flow versus valve displacement for various fluidflows within the controller of the present invention.

FIG. 10 is a graph of amplification ratio versus valve displacement,corresponding to the flow graph of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, which are not intended to limit theinvention, FIG. 1 is a hydraulic schematic of a vehicle hydrostaticsteering system including a fluid controller made in accordance with theteachings of the present invention. The system includes a fluid pump 11,shown herein as a fixed displacement pump, having its inlet connected toa system reservoir 13. The system also includes a pilot operated, loadsensing priority flow control valve, generally designated 15. Thecontrol valve 15 apportions the flow of fluid from the pump 11 between(1) a primary circuit including a fluid controller, generally designated17, and a fluid operated steering cylinder 19; and (2) an open-centerauxiliary circuit, represented by a variable orifice designated 21.

Referring still to FIG. 1 the fluid controller 17 includes an inlet port23, a return port 25, and a pair of control (cylinder) fluid ports 27and 29 which are connected to the opposite ends of the steering cylinder19. The fluid controller 17 further includes a load signal port 31,which is connected to a load signal line 33 which, in turn, is connectedto a load signal port 35 of the priority valve 15, as is well known inthe art.

The priority flow control valve 15 may be of the type illustrated inU.S. Pat. No. 3,455,210, assigned to the assignee of the presentinvention, and incorporated herein by reference. The priority valve 15includes a priority outlet port 37 which is connected to the inlet port23 of the controller 17, and an excess flow outlet port 39 which isconnected to the auxiliary circuit 21. The priority valve 15 includes avalve spool 41 which is biased by a spring 43 toward a positionpermitting substantially all inlet fluid to flow to the priority outletport 37. The spring 43 is aided by the pressure in a signal line 45communicating between the load signal port 35 and the end of the valvespool 41. In opposition to these biasing forces is the pressure exertedby a pilot signal 47, communicated from upstream of the priority outletport 37 to the opposite end of the valve spool 41. The general structureand operation of the priority valve 15 are well known in the art, andbecause they form no direct port of the present invention, they will notbe described further herein.

The fluid controller 17, which will be described in greater detail inconjunction with FIG. 2, may be of the general type illustrated anddescribed in U.S. Pat. No. Re. 25,126, and in the subject embodiment, ismore specifically of the type illustrated and described in U.S. Pat. No.4,109,679, both of which are assigned to the assignee of the presentinvention and incorporated herein by reference. Disposed within thefluid controller 17 is a valving arrangement, generally designated 49,which is movable from its neutral position shown in FIG. 1 to either aright turn position R or a left turn position L. When the valvingarrangement 49 is in either of the turn positions, the pressurized fluidpassing through the valving 49 flows through a fluid meter 51, onefunction of which is to measure (meter) the proper amount of fluid to becommunicated to the appropriate control port 27 or 29. As is well knownto those skilled in the art, the other function of the fluid meter 51 isto provide follow-up movement to the valving 49, such that the valving49 is returned to its neutral position after the desired amount of fluidhas been communicated to the steering cylinder 19. In FIG. 1, thisfollow-up movement is achieved by means of a mechanical follow-upconnection, indicated schematically at 53.

As may best be seen schematically in FIG. 1, the valving arrangement 49defines a plurality of variable orifices whenever the valving 49 ismoved from its neutral position to one of its operating positions,either a right turn position R or a left turn position L. These variableorifices will be described in greater detail subsequently, inconjunction with the detailed description of FIGS. 3 and 4.

Fluid Controller 17

Referring now to FIG. 2, the construction of the fluid controller 17will be described in some detail. The fluid controller 17 comprisesseveral sections, including a housing section 55, a port plate 57, asection comprising the fluid meter 51, and an end plate 59. Thesesections are held together in tight sealing engagement by means of aplurality of bolts 61 which are in threaded engagement with the housingsection 55. The housing section 55 defines the inlet port 23, and returnport 25, (not shown in FIG. 2) and the control ports 27 and 29.

Rotatably disposed within a valve bore 63 defined by the housing section55 is the valving arrangement 49 which is shown schematically in FIG. 1.The valving 49 comprises a primary, rotatable valve member 65(hereinafter referred to as the "spool"), and a cooperating, relativelyrotatable follow-up valve member 67 (hereinafter referred to as the"sleeve"). At the forward end of the spool 65 is a portion having areduced diameter and defining a set of internal splines 69 which providefor a direction mechanical connection between the spool 65 and asteering wheel (not shown). The spool 65 and sleeve 67 will be describedin greater detail subsequently.

The fluid meter 51 may be of the type well known in the art, andincludes an internally-toothed ring 71, and an externally-toothed start73. The star 73 defines a set of internal splines 75, and in splinedengagement therewith is a set of external splines 77 formed at therearward end of a drive shaft 79. The drive shaft 79 has a bifurcatedforward end 81 permitting driving connection between the shaft 79 andthe sleeve 67, by means of a pin 83 passing through a pair of pinopenings (not shown in FIG. 2) in the spool 65. Thus, pressurized fluidflowing through the valving 49 in response to rotation of the spool 65flows through the fluid meter 51, causing orbital and rotationalmovement of the star 73 within the ring 71. Such movement of the star 73causes follow-up movement of the sleeve 67, by means of the drive shaft79 and pin 83 (which comprise the follow-up connection 53 of FIG. 1), tomaintain a particular relative displacement between the spool 65 andsleeve 67, proportional to the rate of rotation of the steering wheel. Aplurality of leaf springs 86 extend through an opening in the spool 65,biasing the sleeve 67 toward the neutral position, relative to the spool65.

Referring still to FIG. 2, it may be seen that the housing section 55defines four annular chambers surrounding the valving 49, to providefluid communication between the valving 49 and the various ports. Anannular chamber 87 receives pressurized fluid from the inlet port 23,while an annular chamber 89 communicates return fluid to the return port25. In addition, an annular chamber 91 provides communication betweenthe valving 49 and the control port 27 while an annular chamber 93provides communication between the valving 49 and the control port 29.

The toothed interaction of the star 73, orbiting and rotating within thering 71, defines a plurality of expanding and contracting fluid volumechambers 95, and adjacent each chamber 95, the port plate 57 defines afluid port 97. The housing section 55 defines a plurality of axial bores99 (only one of which is shown in FIG. 2), each of which is in opencommunication with one of the fluid ports 97. The housing section 55further defines a pair of radial bores 101L and 101R providingcommunication between each of the axial bores 99 and the valve bore 63,as will be described in greater detail subsequently.

Valving Arrangement 49

Referring now primarily to FIG. 4, the spool 65 and sleeve 67 will bedescribed in greater detail. In connection with the subsequentdescription, it should be noted that many of the ports and passages arearranged symmetrically with respect to a central reference plane RP, andsuch elements will be described by a reference numeral followed byeither an R or an L to indicate that the element is located on eitherthe right side or the left side, respectively of the reference plane RP.On the other hand, certain of the elements do not have a correspondingelement oppositely disposed about the reference plane RP and will bereferred to by use of a reference numeral alone. Furthermore, it shouldbe understood that the overlay view in FIG. 4 is intended to illustrateonly the interface between the spool 65 and sleeve 67, and as a result,does not show the various annular chambers 87 through 93 defined by thehousing section 55.

The sleeve 67 defines a plurality of pressure ports 103 (only one ofwhich is shown in FIG. 4), which are disposed to be in continuous fluidcommunication with the inlet port 23 by means of the annular chamber 87.Equally and oppositely disposed about the reference plane RP is aplurality of meter ports 105L, and a plurality of meter ports 105R. Themeter ports 105L are disposed for commutating fluid communication withthe radial bores 101L, while the meter ports 105R are disposed forcommutating fluid communication with the radial bores 101R. Equally andoppositely disposed about the reference plane RP, and further therefromthan the meter ports 105L and 105R, respectively, is a plurality ofoperating ports 107L, and a plurality of operating ports 107R.

Referring still to FIG. 4, the spool 65 defines a pair ofcircumferential meter grooves 111L and 111R, equally and oppositelydisposed about the reference plane RP, and disposed to be axiallyaligned with the meter ports 105L and 105R, respectively. In fluidcommunication with the meter groove 111L is a plurality of pressurepassages 113L and in fluid communication with the meter groove 111R is aplurality of pressure passages 113R. Also in fluid communication withthe meter groove 111L is a plurality of operating passages 115L, and influid communication with the meter groove 111R is a plurality ofoperating passages 115R. In addition to the above-described grooves andpassages which are formed on the outer surface of the spool 6, the spool65 defines a plurality of tank ports 117L, alternately disposed betweenoperating passages 115L, and a plurality of tank ports 117R, alternatelydisposed between operating passages 115R. The tank ports 117L and 117Rare in fluid communication with the interior of the valve spool 65 sothat return fluid passes through the interior of the spool 65 andradially outward through the spring openings into the annular chamber 89which communicates with the return port 25.

Operation of Valving

It is believed that the basic operation of the fluid controller 17 andvalving arrangement 49 described thus far should be readily apparent inview of the teachings of above-incorporated U.S. Pat. No. 4,109,679.However, the operation of the controller and valving will be describedbriefly, partly to relate the structure illustrated in FIGS. 2 and 4 tothe schematic of FIG. 1.

Referring still to FIG. 4, when the valving 49 is in the neutralposition (no rotation of the steering wheel), pressurized fluid iscommunicated from the inlet port 23 to the annular chamber 87, and thenthrough the pressure ports 103. However, with the valving in the neutralposition, flow through the pressure ports 103 is blocked by the outersurface of the spool 65, and there is no fluid flow through the valving49 and fluid meter 51. Therefore, in the subject embodiment, the valving49 is of the type referred to as "closed-center", although it will beapparent to those skilled in the art that the invention is not limitedto closed-center valving. Furthermore, the fluid controller 17 wasdescribed previously in connection with FIG. 1 as being load sensing,although the particular structure by which the valving arrangement 49 isable to communicate a load signal port 31 forms no part of the presentinvention, and is not illustrated or described herein.

When the steering wheel is rotated at a particular speed of rotation,the spool 65 is displaced, relative to the sleeve 67, by a particularrotational displacement which corresponds to the speed of rotation ofthe steering wheel. Thereafter, with continued rotation of the wheel,the fluid flowing through the fluid meter 51 results in follow-upmovement of the sleeve 67 to maintain the particular rotationaldisplacement.

FIG. 5 illustrates the valve spool 65 being displaced, relative to thesleeve 67, which corresponds to moving the valve arrangement 49 of FIG.1 to the right turn position R. With the spool 65 displaced, pressurizedfluid is able to flow from the pressure ports 103 into the respectivepressure passages 113L, the area of overlap therebetween cumulativelycomprising a main variable flow control orifice 121 (see FIGS. 1 and 5)which is commonly referred to as the A₁ orifice. Referring againprimarily to FIG. 4, pressurized fluid flows from each of the pressurepassages 113L into the annular meter groove 111L, then radially outwardthrough the meter ports 105L which are in commutating fluidcommunication with the radial bores 101L, as was described previously.This pressurized, unmetered fluid is then communicated to the fluidmeter 51 through certain of the axial bores 99, the returns from thefluid meter 51 through certain other of the axial bores 99 aspressurized, metered fluid. The metered fluid then flows through theradial bores 101R which are in commutating fluid communication with themeter ports 105R. Metered fluid flowing through the meter ports 105Renters the annular meter groove 111R, then flows into the operatingpassages 115R, the flows through the respective operating ports 107R.The overlap therebetween cumulatively comprising a variable flow controlorifice 123 (see FIG. 1) which is commonly referred to as the A₄orifice.

Fluid flowing through the operating ports 107R enters the annularchamber 93, then flows to the control port 29, then to the right end ofthe steering cylinder 19. Fluid which is exhausted from the left end ofthe steering cylinder 19 is communicated through the control port 27 tothe annular chamber 91, then through the operating ports 107L, andthrough the tank ports 117L, the area of overlap therebetweencumulatively comprising a variable flow control orifice 125 (see FIG.10, which is commonly referred to as the A₅ orifice. As was describedpreviously, return fluid which flows through the tank ports 117L thenflows through the interior of the spool 65, then radially outwardthrough the pin openings to the annular chamber 89, from where fluidflows to the return port 25, and then to the system reservoir 13. Theflow path described above will be referred to hereinafter as the "mainfluid path", and it should be noted by reference to FIG. 1 that the loadsignal port 31 communicates with the main fluid path at a locationimmediately downstream from the main variable flow control orifice 121.It should be apparent that, if the spool is displaced, relative to thesleeve, in the opposite direction, so that the valving 49 is in the leftturn position L, the flow through the valving 49 will be in the"opposite" direction, as that term will be understood from a reading andunderstanding of above-incorporated U.S. Pat. No. 4,109,679.

Amplification Fluid Path

Referring now primarily to FIG. 4, the added elements which provide forthe amplification fluid path of the present invention will be described.It should be noted that all of the elements described up to this pointare elements which are already known, and have been illustrated anddescribed in above-incorporated U.S. Pat. No. 4,109,679. The sleeve 67defines two pairs of amplification bores 127 (only one pair being shownin FIG. 4), with the bores 127 in each pair being centered with respectto the central reference plane, as shown in FIG. 4.

Referring now to FIG. 4, in conjunction with the flow diagram of FIG. 3,the operation of the present invention will be described generally.Pressurized fluid in the annular chamber 87 is present in the bores 127,but communication therethrough is blocked by the outer surface of thespool 65, just as communication through the pressure ports 103 isblocked by the outer surface of the spool 65, when the valving is inneutral. As the spool 65 is displaced, relative to the sleeve 67,eventually pressurized fluid is able to flow through the amplificationbores 127 into the adjacent pressure passages 113R, the area of overlaptherebetween cumulatively comprising a variable amplification orifice129 (see FIG. 3) which may also be referred to as the A_(A) orifice. Thepressurized fluid flowing through the amplification orifice 129 flowsfrom the pressure passages 113R into the annular meter groove 111R,there combining with the fluid which has passed through the fluid meter51 and through the meter ports 105R. This combined quantity of fluidthen flows into the operating passages 115R, and then through theoperating ports 107R, as described previously.

Referring now primarily to FIG. 3, the amplification fluid pathdescribed above is, in the subject embodiment, in communication with themain fluid path at a location upstream of the main variable flow controlorifice 121. The fluid flowing through the amplification fluid path, andthrough the variable amplification orifice 129 then recombines with themain fluid path at a location upstream of the variable flow controlorifice 123. It will be understood by those skilled in the art that,when practicing the present invention, it would be necessary to increasethe flow capacity of the variable orifice 123 to accommodate the totalflow through both the main fluid path and the amplification fluid path.

Referring still to FIG. 3, several possible applications for the presentinvention will be described. Shown schematically in FIG. 3 is adampening fluid path 131, including a variable dampening orifice 133.The path 131 is connected to the main fluid path at a locationdownstream of the variable orifice 123, and is able to communicate asmall amount of dampening fluid, through the variable dampening orifice133, to the return side of the main fluid path, downstream of thevariable flow control orifice 125. A more detailed description of theconstruction and operation of the dampening fluid path 131 is providedin copending application U.S. Ser. No. 037,493, filed Apr. 13, 1987, nowU.S. Pat. No. 4,781,219, in the name of Donald M. Haarstad and DouglasM. Gage, for an Improved Fluid Controller and Dampening Fluid Path.

The dampening fluid path 131 has been found to be effective forcushioning or dampening pressure pulses and spikes in the lines betweenthe controller 17 and the steering cylinder 19. However, the flowthrough the dampening fluids path 131 does represent a loss form thesystem, thus decreasing the flow to the steering cylinder 19, andincreasing the number of turns of the steering wheel lock to lock.Therefore, one application of the present invention is to size thevariable amplification orifice 129 to be approximately equal to thevariable dampening orifice 133, such that the quantity of amplificationfluid which bypasses the fluid meter 51 is approximately equal to theamount of dampening fluid, and the net flow of fluid to the steeringcylinder 19 will be the same as the flow through the meter 51.

Alternatively, another application for the present invention is toprovide true flow amplification, such that whether or not the controller17 includes a dampening fluid path 131, the variable amplificationorifice 129 is sized such that the net flow to the steering cylinder 19is substantially greater than the flow through the fluid meter 51. Theamplification aspect of the present invention will be describedsubsequently in connection the graphs in FIGS. 9 and 10.

A more detailed description of the operation of the invention will nowbe provided. Referring primarily to FIG. 5-7 in conjunction with thegraph of FIG. 9, it should be noted that in each of FIGS. 5-7, there isincluded an indication of the number of degrees of relative rotationbetween the spool 65 and sleeve 67. It will be understood by thoseskilled in the art that the particular displacements illustrated, aswell as the shape of each of the "gain" curves in FIG. 9 is by way ofexample only, and the invention is not limited to any particular shapeof gain curve, nor to any particular relationship between valvedisplacement and opening and closing of the various orifices.

Referring now to FIG. 5, the spool 65 has been displaced by about 4degrees relative to the sleeve 67, and each of the pressure ports 103 isjust beginning to communicate with its respective pressure passage 113L.Therefore, the main variable flow control orifice 121 is just beginningto open as may be seen in the graph of FIG. 9 (flow curve labeled"121"). At this particular valve displacement, communication between theamplification bores 127 and the pressure passage 113R is still blocked,such that there is no flow through the amplification fluid path.

Referring now to FIG. 6, the spool 65 has been displaced by about 7degrees relative to the sleeve 67. At this particular valvedisplacement, there is substantial communication between the pressureports 103 and the pressure passages 113L (i.e., through the mainvariable flow control orifice 121), and at the same time, theamplification bores 127 are in full communication with the pressurepassages 113R. As the variable amplification orifice began to open at 4degrees of displacement, the total flow out of control port 29 (flowcurve labeled "29") began to exceed the flow through the main variableflow control orifice 121.

When the spool 65 is displaced by about 10 degrees relative to thesleeve 67 (the position shown in FIG. 7), the amplification bores 127are completely blocked from fluid communication with the pressurepassages 113R. The result is that the variable amplification orifice 129is closed at a displacement of 10 degrees which, in the subjectembodiment, is the maximum possible displacement of the spool 65relative to the sleeve 67.

As may be seen in the graph of FIG. 9, when the valving is displaced byabout 7 degrees, the flow through the main variable orifice 121 isapproximately 3.3 gpm, and the total flow is approximately 6 gpm.Therefore, in the subject embodiment, after the variable amplificationorifice 129 is fully open, at about 7 degrees displacement, the flowthrough the amplification fluid path is approximately 2.7 gpm. As thevalving is further displaced, the amplification flow gradually decreasesto zero, as the flow through the main fluid path continues to increase,such that the total flow decreases slightly from about 6.0 gpm to about5.8 gpm, when the valving reaches its maximum displacement, as shown inFIG. 7.

Manual Steering

It is an essential feature of the present invention that theamplification fluid path increases in flow capacity until the valvingreaches its normal operating position which, in the subject embodiment,is a displacement of about 7 or 8 degrees of the spool 65 relative tothe sleeve 67. As is well known to those skilled in the art, in a manualsteering mode of operation, rotation of the steering wheel results inmaximum deflection of the spool 65 relative to the sleeve 67, becausethe amount of torque required to generate pressurized fluid (in a manualsteering mode, the controller is effectively operating as a hand pump)is always enough to overcome the force of centering springs 86.

In connection with the development of the present invention, it wasfound that the use of an amplification fluid path, as illustrated anddescribed in U.S. Pat. No. 4,759,182 would eliminate the ability tomanually steer, i.e., generate pressurized fluid by rotating thesteering wheel. It was subsequently discovered that the prior artamplification fluid path would effectively serve as a "short-circuit",whereby pressurized fluid generated by rotation of the fluid meter 51would flow back through the amplification bores 127 to the inlet port 23of the controller.

In accordance with the present invention, whenever the controller isbeing operated in a manual steering mode, and the valving is at itsmaximum displacement as shown in FIG. 10, the amplification bores 127are out of fluid communication with the pressure passages 113R (i.e.,assuming right turn condition). Therefore, pressurized fluid generatedby rotation of the fluid meter 51 is communicated back through the meterports 105R into the meter groove 111R. The pressurized fluid flowsthrough the operating passages 115R, and through the operating ports107R (variable flow control orifice 123), then out through the cylinderport 29 to the cylinder 19 to effect operation thereof. However, duringthe manual steering operation as described, the pressurized fluid in theannular meter groove 111R is able to flow into the pressure passage113R, but is blocked from communication with the amplification bores 127which, as shown in FIG. 7 are not communicating therewith. In otherwords, the amplification orifice 129 is closed during operation in themanual steering mode.

As a result of the present invention, it is possible to utilize acontroller having a fluid meter with a volume of approximately 6 cubicinches per revolution, and it will have the normal manual steeringcapability of a 6 cubic inch controller, but will have the powersteering capability of a controller having approximately a ten cubicinch meter.

Amplification Ratio

Referring now to the graph of amplification ratio versus valvedisplacement in FIG. 10, in conjunction with FIGS. 5-7, the followingperformance characteristics should be noted:

(1) Because the pressure ports 103 begin to open at 3 degrees but theamplification bores 127 do not open until 4 degrees, minor steeringcorrections can be made without any amplification flow (i.e.,amplification ratio equal to 1.0), such that the steering is not overlyresponsive at small wheel deflections;

(2) The amplification flow reaches its maximum at 7 degrees of valvedisplacement, such that the amplification ratio is at its peak (between1.8 an 2.0) for valve displacements between about 6 degrees and 7degrees, corresponding to typical steering action; and

(3) Because the amplification flow does not continue to increase afterabout 7 degrees of valve displacement, but the flow through the mainfluid path (flow curve 121) does continue to increase, the amplificationratio gradually decrease as the valve displacement moves toward themaximum, thus avoiding overly responsive steering at high steeringinputs.

FIG. 8 Embodiment

Referring now to FIG. 8, there is illustrated schematically analternative embodiment of the present invention in a flow diagramsimilar to FIG. 3. The embodiment of FIG. 8 differs from that of FIG. 3in several ways.

First, the controller 17 of FIG. 3 is of the type described in U.S. Pat.No. 4,109,679, in which the spool and sleeve define only three variableflow control orifices (121; 123; and 125). The embodiment of FIG. 8includes a controller 140 of the type described in U.S. Pat. No. Re.25,126 in which the spool and sleeve define a main variable flow controlorifice 141 (A₁); variable flow control orifices 142 (A₂) and 143 (A₃),immediately upstream and downstream of the fluid meter 51, respectively;a variable flow control orifice 144 (A₄) upstream of the control port29; and a variable flow control orifice 145 (A₅) downstream of thecontrol fluid port 27 on the return side.

Secondly, in the embodiment of FIG. 3, the amplification fluid pathcommunicates with the main fluid path upstream of the main variable flowcontrol orifice 121. In the embodiment of FIG. 8, partly because thereare variable flow control orifices 142 and 143 on either side of thefluid meter 51, the amplification fluid path communicates with the mainfluid path downstream of the main variable flow control orifice 141.Therefore, in the embodiment of FIG. 8, the variable orifices 141 and144 must be sized for the entire steering flow.

The invention has been described in great detail in the foregoingspecification, and it is believed that various alterations andmodifications of the invention will become apparent to those skilled inthe art from a reading and understanding of this specification. It isintended that all such alterations and modifications are included in theinvention, insofar as they come within the scope of the appended claims.

I claim:
 1. A controller operable to control the flow of fluid from asource of pressurized fluid to a fluid pressure operated device; saidcontroller being of the type including housing means defining an inletport for connection to the source of pressurized fluid, a return portfor connection to a reservoir, and first and second control fluid portsfor connection to the fluid pressure operated device; valve meansdisposed in said housing means and defining a neutral position and afirst operating position; said housing means and said valve meanscooperating to define a main fluid path communicating between said inletport and said first control fluid port, and between said second controlfluid port and said return port when said valve mean is in said firstoperating position; fluid actuated means for imparting follow-upmovement to said valve means proportional to the volume of fluid flowthrough said fluid actuated means, said fluid actuated means beingdisposed in series flow relationship in said main fluid path betweensaid inlet port and said first control fluid port; said main fluid pathincluding a first variable flow control orifice disposed between saidinlet port and said fluid actuated means, and having its minimum flowarea when said valve means is in said neutral position, and anincreasing flow area as said valve means is displaced from said neutralposition toward said first operating position; said main fluid pathincluding a second variable flow control orifice disposed between saidfluid actuated means and said first control fluid port; said housingmeans and said valve means cooperating to define an amplification fluidpath, in parallel with said main fluid path, said amplification fluidpath being in fluid communication with said main fluid path at a firstlocation disposed between said fluid inlet port and said first variableflow control orifice, and at a second location disposed between saidfluid actuated means and said first control fluid port; saidamplification fluid path including a variable amplification orificehaving a substantially zero flow area when said valve means is in saidneutral position, and an increasing flow area as said valve means isdisplaced from said neutral position toward said first operatingposition; and said main variable flow control orifice begins to open atleast as soon as said variable amplification orifice, as said valvemeans moves from said neutral position toward said first operatingposition; said main variable flow control orifice having its maximumflow area when said valve means is displaced from said neutral positionto a maximum displacement position; characterized by:(a) said variableamplification orifice reaching its maximum flow area when said valvemeans is displaced from said neutral position to said first operatingposition, at substantially less than said maximum displacement position;and (b) said variable amplification orifice changes from its maximumflow area to said substantially zero flow area as said valve means isdisplaced from said first operating position to said maximumdisplacement position.
 2. A controller a claimed in claim 1characterized by said valve means comprising a primary, rotatable valvemember and a cooperating, relatively rotatable valve member, saidprimary and follow-up valve members defining said neutral positionrelative to each other.
 3. A controller as claimed in claim 2characterized by said primary and follow-up valve members cooperating todefine said first and second variable flow control orifices, the flowareas of said variable orifices varying in response to relative rotationof said primary and follow-up valve members.
 4. A controller as claimedin claim 2 characterized by said amplification fluid path and saidvariable amplification orifice being wholly defined by said primary andfollow-up valve members.
 5. A controller as claimed in claim 2characterized by said fluid actuated means comprises a fluid meterincluding a metering member movable to measure the volume of fluidflowing through said main variable flow control orifice, said controllerfurther comprising means coupling said metering member to said follow-upvalve member.
 6. A controller as claimed in claim 1 characterized bysaid simplification fluid path being in fluid communication with saidmain fluid path at a second location disposed between said fluidactuated means and said second variable flow control orifice.
 7. Acontroller as claimed in claim 1 characterized by said first variableflow control orifice and said variable amplification orifice begin toopen at approximately the same amount of displacement of said valvemeans from said neutral position.
 8. A controller as claimed in claim 1characterized by said first variable flow control orifice beings to openbefore said variable amplification orifice begins to open as said valvemeans moves from said neutral position toward said operating position.9. A controller as claimed in claim 1 characterized by the source ofpressurized fluid including a fluid pump and pressure responsive meansfor varying the delivery of fluid to said controller in response tovariations in demand for fluid by said controller, said housing means ofsaid controller defining a load signal port for connection to thepressure responsive means, said load signal port being in fluidcommunication with said main fluid path at a location disposeddownstream of said first variable flow control orifice.
 10. A controlleras claimed in claim 9 characterized by the pressure responsive meanscomprising a priority flow control valve disposed in series flowrelation between the pump and said controller, the priority flow controlvalve including an inlet port in fluid communication with the pump, apriority outlet port in fluid communication with the inlet port of saidcontroller, an excess flow outlet port adapted for fluid communicationwith an auxiliary load circuit, and a priority valve member movablebetween one position permitting substantially unrestricted fluidcommunication from said inlet port of said priority valve to saidpriority outlet port, and another position permitting substantiallyunrestricted fluid communication from said inlet port to said excessflow outlet port, means biasing said priority valve member toward saidone position, said biasing means including means providing fluidcommunication with said load signal port of said controller.